Total hip replacement (THR) relieves pain for ten to twenty years in over 90% of patients with disabling hip arthritis. These excellent results have been reported almost exclusively from large referral centers, yet over half of primary THRs and three quarters of revision THRs occur in hospitals which perform fewer than one of these procedures per week in the US Medicare population. We do not know whether the achievements of referral centers have been translated effectively to smaller hospitals where most THRs are now performed. The aims of this study are to 1) document the outcomes of primary and revision THR in a population based cohort of elderly Americans, including mortality, complications, symptoms, functional status, and hospitals with a higher volume of THR have better outcomes. This study employs an innovative design which has never been applied in health services research of a musculoskeletal disorder. We will use Medicare claims data to identify the 80,000 beneficiaries over 65years old in the US who had primary THR and 15,000 who had revision THR in 1995. Claims data will provide rates of mortality and complications. A random sample of 1000 primary THRs and 1000 revisions from five states will be selected for detailed study. This includes medical record review to obtain information on the operative procedure, preoperative comorbidity and complications; and patient interview three years after surgery to obtain information on symptoms, function and satisfaction. Data on the hospitals and surgeons involved in these case will be obtained from surveys. Our analyses will focus upon potential correlates of outcomes with particular attention to associations between outcome and hospital and surgeon volume of THR.